Device for the electrolytic deposition of metal on metal strips

ABSTRACT

In a device for the electrolytic deposition of metal on the metal strips (1) forming the cathode, which are taken through a gap in an electrolyte (3) between two flat or rod-like parallel anodes (2), the proposal is for edge masks (4) to screen off the edge regions of the metal strip (1). The shanks (41 ) of each edge mask (4) are prestressed by springs against the anodes (2) and their relatively wide shanks may be directed transversely to the direction of the strip in order to take transitions between different strip widths into account.

The invention relates to a device for the electrolytic deposition ofmetal on the metal strips forming the cathode, preferably steel strips,in accordance with the introductory part of claim 1.

A device of said type is known, in which for the prevention of irregularand excessive deposition of the metal on a metal strip to be galvanized,provision is made in the gap between each two parallel, plate-likeanodes for edge masks having a U-shaped cross section, which masks, withtheir two shanks extending parallel with each other, such shanks beingsuitably set up transversely to the direction of the strip, enclose theedge zones of the metal strip to be coated, and thus screen off saidzones against the electrical field, so that the deposition occurring inthe respective edge zones of the metal strip is not stronger than theother deposition on the strip. Said edge masks are made of an insulatingmaterial, preferably of plastic material. In view of the relativelylarge anode plates, said plastic masks with a U-shaped cross sectionhave a length of up to two meters and are, therefore, relativelyunstable, corresponding to the small gap between the strip and theanodes, so that only relatively small shank widths can be formed. It isnecessary in practical life to coat in strip refining plants stripcharges with different widths of the strips. After the strips of acertain widths--which, as a rule, run off coils--have been treated, itis, therefore customary to weld the next strip to the end. Such nextstrip may have a different width. For the purpose of adapting thescreening of the edge zone to the next-following strip to be coated, theedge masks can be set up transversely to the direction of the strip.When the next-following strip is inserted between the two shanks of theedge masks, the zone of transition of the strip with the break in widthcauses problems in this connection. Since the shanks of the edge maskshave only a relatively short length, it happens that the next-followingstrip will not "thread" itself between the two shanks but is guidedbetween the outer side of a shank and the adjacent anode, which candestroy the edge masks and damage the anodes. However, the width of theshanks of the known edge masks cannot be enlarged, as this will make theedge mask too unstable. In addition, the electrolyte flows through thegap between the anodes still at a relatively high rate, whereby apressure difference is caused between the inside and the outside of eachmask shank due to differences in flow pressure, such pressure differencesubjecting the shank to an inwardly directed pressure. Therefore, shankswith low stiffness, if excessively long, are forced inwardly and therebynarrow the clear spacing between the shanks. With the known masks withthe relatively short shanks, there is the additional risk that thesheets to be coated knock in an undesirable way against the inside ofthe shanks or against the bridge of the masks due to their tolerances inguidance and because of uneven spots, and thus may even damage ordestroy the masks. Therefore, only masks with a small outside dimensioncan be used in the narrow gap, which amounts to about between 20 mm to50 mm. It is not possible to visually monitor the masks in the devicefrom the outside.

The object of the invention is to enhance on a device of the typespecified above the edge masks in order to particularly assure thescreening in a deposition process after changing from one strip toanother of a different width.

The object of the invention is solved on a device of the type specifiedabove, such device being characterized in that the shanks of each edgemask rest against the anodes with elastic prestress.

If edge masks according to the invention are correspondingly arrangedbetween the anodes, it is possible due to the predetermined elasticprestress to realize substantially greater widths of the shanks of theedge mask made of suitably insulating material because on the one hand,by having the shanks rest against the anodes under elastic prestress, amore stable position of the edge masks within the gap is obtained and,therefore, an additional support of such masks. On the other hand, thepressure difference caused by the flow of the electrolyte on the shanksis counteracted by the prestress in a compensating manner. The springybutting of the shanks of the edge mask provides for a total screening ofthe edge zone of the metal strip against any possible electrical fieldfrom the outside of the anodes outside the zone of the strip width.

Therefore, with devices having the edge masks according to theinvention, it is possible to realize relatively large shank widths of upto 200 mm, so that the usable depth of the edge mask is much greaterthan with conventional edge masks. Therefore, with such a relativelydeep edge mask it is possible also to bridge without problems breaks instrip width without running the risk that the next-following strip of adifferent width will "thread" itself "out" of such an edge mask.

Preferably, corresponding edge masks should have a V-shaped crosssection, whereby the apex of the "V" may also form a bridge connectingthe shanks.

The associated drawing shows in cross section a basic view of the zoneof the two anodes kept spaced apart, whereby the metal strip to becoated is passed in an electrolyte through about the center of the gapspacing said anodes apart.

The two anodes are denoted by reference numeral 2. The metal strip to becoated, which has a smaller width, is denoted by the referencenumeral 1. The electrolyte is indicated by reference numeral 3. The edgemasks made of an insulating material, which are denoted by numeral 4,are arranged in the gap transversely to the direction of the metalstrip 1. Said edge masks have a V-shaped cross section. Their two shanks41 rest under elastic prestress against the insides of the anodes 2 andenclose the edge zone of the metal strip 1 in order to screen it offagainst a maintained electrical field. The two shanks 41 are connectedwith each other by a bridge 42. The way in which said edge mask 4 can beset up for adapting it to different strip widths is indicated by the twoarrows.

We claim:
 1. Device for the electrolytic deposition of metal on acathode formed by a metal strip, comprisingtwo plate-like or rod-likeanodes arranged parallel to each other with a gap therebetween; saidmetal strip being guided through said gap in an electrolyte adopted tobe between said two anodes; two edge masks each having two shanks forenclosing in a screening way the edge zone of the metal strip and set upin said gap transversely to the direction of the strip; and said shanksof each edge mask rest against the anodes with elastic prestress. 2.Device according to claim 1,wherein the edge masks have a V-shaped crosssection.
 3. Device according to claim 2,wherein the apex of the "V"forms a bridge connecting the shanks.
 4. Device according to claim1,wherein said edge masks are adjustable transversely to the stripdirection.